1. Field
The invention relates to the creation of green tire blanks by winding strips onto a member exhibiting symmetry of revolution.
2. Description of Related Art
Document EP-0 264 600 discloses a device for creating a green tire blank which comprises a rotary drum and a tool having an arm able by extrusion to produce a strip and wind it onto the drum. The arm is articulated to its support about an axis parallel to the axis of rotation of the drum. Thus, the arm can adapt its position in the direction radial to the axis of the drum in order to move closer or further away to account for irregularities in the shape of the drum or of the winding already laid and also in order to follow the increase in diameter of the green tire blank caused by the build-up of the layers of strip already laid.
In addition, the arm is able to move in rotation with respect to the support about an axis parallel to the longitudinal direction of the arm so that the orientation of the strip can be adapted to its position on the tire, for example on the sidewalls of the green tire blank or alternatively so that it can be superposed in full or in part with one or more layers of strip already laid.
The arm is also mounted with the ability to slide so that it can travel across the entire width of the green tire blank.
When the strip is being wound, the arm applies to it an application force in order to cause it to stick to the layers of strip already wound. However, the weight of the arm, which bears the extrusion means and sometimes even drive means, applies an additional force to the strip. This force has little adverse consequence when the cross section of the strip has its largest dimension parallel to the axis of rotation of the drum. By contrast, it does have adverse consequences when the strip is laid in a position that is inclined with respect to that axis.
This is because the application force and the effect of gravity, in such a case, are not parallel and their resultant therefore has a component parallel to the axis of rotation of the drum. This can deform or harm the strip as it is being laid.
In addition, the degree of precision usually required for positioning the strip on the green tire blank is of the order of one tenth of a millimetre.
Reducing the cycle times involved in manufacturing such a green tire blank means that the speed at which the receiving surface rotates and the strip feed rate are speeded up. The receiving surface on which the green tire blank is built is a surface of revolution which may have a cylindrical or toroidal overall shape.
In order to adapt the position of the strip it is therefore desirable to be able to make the arm pivot about the centre of the strip at a high angular acceleration.
Now, since the mass carried by the arm is itself high, the moment of inertia of the arm about this axis may reach values that are not insignificant.
Bearing in mind the desired acceleration values, the resistive torque that appears as the arm rotates may have a significant effect on the mechanical forces on the axes.
Now, the technologies that allow such a torque to be transmitted have two significant disadvantages. They generate a high bulk and they substantially increase the overall mass of the device. Further, if assembly clearances that are small enough to be compatible with the installation are desired, the additional costs involved are great.